Liquid-sealing type vibration isolating apparatus

ABSTRACT

The liquid-sealing type vibration isolating apparatus of the present invention includes a coupler configured to be attached to a vibrating body, a holder, an insulator for absorbing and isolating vibration from the vibrating body at a position between the coupler and the holder, and a vibration isolating mechanism directly following the insulator and including liquid chambers sealing an incompressible fluid. This vibration isolating mechanism has a main chamber sealing a liquid, having a part of a wall thereof formed by the insulator, an auxiliary chamber communicating with the main chamber via an orifice, and an equilibrium chamber provided in a portion of the main chamber via a diaphragm and having a varying volume in the chamber. The vibration isolating apparatus further includes a switching mechanism for introducing a negative pressure and the atmospheric pressure continuously or in synchronization with vibration of the vibrating body, and a control mechanism for controlling this switching operation.

This application is a continuation of U.S. Application Ser. No.09/033,481, filed Mar. 3, 1998, now U.S. Pat. No. 6,176,477, which is acontinuation-in part of U.S. Application Ser. No. 08/859,112, filed May20, 1997, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of The Invention

The present invention relates to a liquid-sealing type vibrationisolating apparatus which gives a vibration isolating effect on thebasis of the flowing action of a fluid (liquid) sealed therein. Moreparticularly, the present invention relates to a liquid-sealing typevibration isolating apparatus in which the liquid in a liquid chamber isvibrated at a certain frequency, the vibrating apparatus thereof havinga simple structure, and isolation of vibration of a plurality of kindsis effectively accomplished over a wide scope ranging from low to highfrequency regions.

2. Description of The Related Art

A vibration isolating apparatus, particularly an automotive engine mountmust be capable of coping with a wide range of frequencies because theengine serving as a power source is used under various conditionsranging from idling operation to the maximum velocity of revolutions.For this purpose, there has already been invented an apparatus known asa liquid-sealing type engine mount (vibration isolating apparatus) inwhich two liquid chamber are provided and are connected with an orifice,such as the one disclosed in Japanese Unexamined Patent Publication No.4-60231.

The aforesaid known apparatus is designed to have two orifices to copewith two kinds of input frequency within the low-frequency region. Theapparatus can cope (vibration isolation) with two kinds of vibrationsuch as engine idling vibration and engine shaking by operating thesetwo orifices. These kinds of vibration have however a frequency with arange of from 10 to 30 Hz. An automobile engine is used under diverseand various circumstances, and the range of frequencies of vibration andnoise propagating through the engine and the engine mount supporting theengine covers a wide region. Recently, in particular, vibration andnoise associated with engine noise including a dull sound which is avibration within the higher frequency region, in addition to theforegoing idling vibration and engine shake are forming an issue.

More recently, tuning of an engine mount is becoming more common with aview to isolating a dull sound associated with vibration of a relativelyhigh frequency within a range of from 100 to 600 Hz. For the purpose ofcoping with a plurality of conditions as described above, there hasalready been known a liquid-sealing type vibration isolating apparatushaving a liquid chamber and a fluid bag to change the volume at aspecific frequency within the fluid bag, as disclosed, for example, inJapanese Patent Publication No. 6-29634.

In this known apparatus, the fluid bag is provided in the liquid chamberto change the volume thereof at a prescribed frequency, thereby causinga liquid in the liquid chamber on the vibration input side to flow viaan orifice toward another side liquid chamber. More specifically, in thelow-frequency region mainly comprising idling vibration, the liquidpressure in the liquid chamber on the vibration input side is increasedso as to obtain a high damping property. In the high-frequency region,on the other hand, increase in the liquid pressure in the liquid chamberon the vibration input side is avoided to obtain a low dynamic springconstant. For recent automotive engine mounts, however, a vibrationisolating apparatus should cover idling vibration against whichresonance phenomenon should be avoided by reducing the dynamic constantas vibration within the low-frequency region, and vibration associatedwith engine shaking against which vibration should be inhibited byincreasing the damping property.

Further, in this known apparatus, a fluid pressure generating device isneed for causing the volume thereof to be changed, so that there areraised the following problems.

(1) An additional space has to be secured in an engine room.

(2) The apparatus itself increases a production. cost.

In order to achieve a vibration isolating apparatus capable of copingwith these contradictory conditions, simple vibrating of the liquid inthe liquid chamber on the vibration input side in the same or reversedphase is insufficient.

To cope with these multiple conditions, furthermore, there is alreadyknown an apparatus called a voice-coil type liquid-sealing typevibration isolating apparatus in which a liquid chamber is provided andwhich has a vibrator comprising a voice coil or the like vibrating at acertain frequency in the liquid chamber, as-disclosed, for example, inJapanese Unexamined Patent Publication No. 5-149369. An apparatus ofthis type has however inevitably a complicated structure because of thenecessity of a plurality of liquid chambers, a movable piece comprisinga piston or the like in the liquid chamber and a voice coil for drivingsuch a movable piece. The vibration isolating apparatus as a wholebecomes unavoidably heavier because of shaking coils, permanent magnetsand many other parts.

SUMMARY OF THE INVENTION

The present invention was developed to solve the problems as describedabove, and has an object to provide a vibration isolating apparatuscapable of certainly inhibiting vibration occurring from a vibratingbody from propagating in the vehicle room.

Another object of the present invention is to provide a liquid-sealingtype vibration isolating apparatus permitting giving a low dynamicspring constant even in the high frequency region for the purpose ofisolating vibration in a relatively high frequency region.

Further another object of the present invention is to provide aliquid-sealing type vibration isolating apparatus which can give a lowdynamic spring constant (low dynamic spring property) for both vibrationin a low-frequency region mainly comprising idling vibration andvibration in a high-frequency region causing a dull sound, and give ahigh damping property against vibration in a low-frequency region comingfrom engine shake.

To achieve these objects, according to the present invention, aliquid-sealing type vibration isolating apparatus is provided whichcomprises a coupler attached to a vibrating body, a holder attached tothe vehicle body side, an insulator which is provided between thecoupler and the holder and absorbs and isolates vibration from thevibrating body, and a vibration isolating mechanism which directlyfollows the insulator and is formed with a liquid chamber sealing aliquid which is an incompressible fluid; the vibration isolatingmechanism comprising a main chamber having a wall thereof formed by apart of the insulator and sealing the liquid, an auxiliary chamberconnected to the main chamber so that the liquid flows through anorifice, an equilibrium chamber which is provided at a part of the mainchamber via a diaphragm and is formed so that the volume thereof in thechamber changes, and an air chamber which surrounds the auxiliarychamber via another diaphragm and constantly receives air; wherein thereare further provided switching means which conducts a switchingoperation so as to alternately introduce any one of a negative pressureand the atmospheric pressure into the equilibrium chamber having theaforesaid construction constantly or in synchronization with enginevibration, and in addition, control means which controls the switchingoperation of the switching means.

By adopting the constitution as described above, the following effectsare available in the present invention. In the present invention, morespecifically, an equilibrium chamber is provided via a diaphragm in themain chamber, and a negative pressure or the atmospheric pressure isappropriately introduced into the equilibrium chamber. Introduction ofthe negative pressure or the atmospheric pressure is accomplishedthrough switching means under control by the control means. That is,operation of this switching means causes the negative pressure to beperiodically introduced at a certain frequency or causes a certainnegative pressure to be continuously introduced. As required, theequilibrium chamber is kept in a state open to the open air. Therefore,in response to idling vibration of the engine forming a vibrating body,the pressure (volume) of the equilibrium chamber is altered through anON/OFF operation of the switching means, thereby absorbing fluctuationsof the liquid pressure in the main chamber caused by idling vibrationentered via the insulator. This results in a reduced dynamic springconstant of the spring system formed by the insulator and the vibrationisolating mechanism. Idling vibration is thus absorbed and isolated.

To cope with high-frequency vibration within a range of from 100 to 600Hz causing a dull sound, which is a problem during travel of a vehicle,the switching means is operated to bring the equilibrium chamber into astate open to the open air. As a result, the volume in the equilibriumchamber freely changes relative to high-frequency vibration entered viathe insulator and the liquid in the liquid chamber. This permits freevibration of the insulator and the liquid in the liquid chamber, wherebythe dynamic spring constant of the spring system formed by the vibrationisolating mechanism is inhibited to a low level. An improved isolatingeffect is thus available against high-frequency vibration. In thepresent invention, as described above, the switching means comprising aswitching valve or the like, the orifice and the equilibrium chamberpermit absorption and isolation of multiple kinds of vibration.

The liquid is allowed to flow through an orifice connecting the mainchamber and the auxiliary chamber to isolate engine shake which isvibration of a frequency further lower than idling vibration, therebyabsorbing and isolating the engine shake. More specifically, sincevibration associated with engine shake has a frequency of about 10 Hz,it is difficult to isolate vibration by reducing the dynamic springconstant. In the present invention, therefore, a certain negativepressure is introduced into the equilibrium chamber forming thevibration isolating mechanism so as to bring the volume of theequilibrium chamber to null. This allows the liquid to flow through anorifice formed between the main chamber and the auxiliary chamber, andviscous drag resulting from the liquid causes production of a prescribeddamping force. This damping force leads to damping of engine shake.

In another means for achieving the foregoing objects, a vibrationisolating mechanism comprising a liquid chamber and the like is providedin series with the insulator. More particularly, there is provided aliquid-sealing type vibration isolating apparatus, wherein the vibrationisolating mechanism comprises a main chamber which comprises a liquidchamber arranged in series with the insulator and having a wall thereofformed by a part of the insulator, an auxiliary chamber connected to themain chamber so as to allow the liquid to flow via an orifice to themain chamber and separated by a partition plate comprising a rigid bodyfrom the main chamber, an equilibrium chamber formed via a diaphragmbetween the main chamber and the partition plate and arranged so as tointroduce any one of the atmospheric pressure and a negative pressure,and an air chamber provided under the auxiliary chamber via anotherdiaphragm and constantly fed with air. By adopting this configuration,in the present invention, vibration from the vibrating body istransmitted directly to the insulator and the liquid in the mainchamber, thus further improving the vibration isolating effect, inaddition to the foregoing means. A vibration isolating apparatus havingan equilibrium chamber in the main chamber is formed on the basis of theconventional upright-type liquid-sealing type vibration isolatingapparatus, thus permitting improvement of assembly merit of thevibration isolating apparatus as a whole.

The aforesaid objects are achieved according to the present inventionalso by the vibration isolating apparatus, wherein the length L1 of aduct line from the atmospheric pressure inlet to the equilibrium chamberis set at a value determined by the following formula:

0.85cT/4≦L 1≦1.15cT/4

where c is the sound velocity (340 m/sec) and T is a period of time (inseconds) during which the open air is introduced into the equilibriumchamber by the switching means.

The foregoing objects are achieved, according to the present invention,in the vibration isolating apparatus of the above-mentionedconfiguration, by providing an expansion chamber having a largerdiameter than that of the duct line between the atmospheric pressureinlet and the switching means and setting the length L2 between theexpansion chamber and the equilibrium chamber at a value determined bythe following formula:

0.85cT/4≦L 2≦1.15cT/4

where c is the sound velocity (340 m/sec) and T is a period of time (inseconds) during which the open air is introduced into the equilibriumchamber by the switching means.

According to the vibration isolating apparatus of the present invention,furthermore, the coupler attached to the vibrating body and theinsulator provided between the coupler and the holder attached to thevehicle body side absorb most of vibration transmitted from thevibrating body. The vibration isolating mechanism following directly theinsulator further controls and absorbs vibration. In other words, theliquid sealed in the main liquid chamber and the auxiliary liquidchamber flows through the orifice under the effect of vibration, andthis flow controls and absorbs vibration. At the same time, a negativepressure introduced from the negative pressure source and theatmospheric pressure introduced from the atmospheric pressure inlet arealternately introduced into the equilibrium chamber provided in aportion of the main liquid chamber via a diaphragm. This introduction isaccomplished by a switching operation of the switching means undercontrol by the control means at a frequency f required for synchronizingwith vibration of the aforesaid vibrating body. This alternateintroduction permits alternate introduction of the negative pressure andthe atmospheric pressure at a frequency corresponding to the requiredfrequency, and in response to this, the pressure in the equilibriumchamber, and hence the volume thereof change. This change in volumepositively controls and absorbs changes in the liquid pressure in themain liquid chamber produced by vibration of the vibrating body andentered via the insulator.

Because the switching means is ,switched over by switching, thisswitching may cause generation of a harmonic component. In the presentinvention, however, the length L1 of the duct line from the atmosphericpressure inlet to the equilibrium chamber is set at a value determinedby the following formula:

0.85cT/4≦L 1≦1.15cT/4

where c is the sound velocity (340 m/sec) and T is a period of time (inseconds) during which the open air is introduced into the equilibriumchamber by the switching means. A pulse may therefore be produced in theair introduced from the atmospheric pressure inlet, resulting in atemporary inertial supercharging. A pressure higher than the atmosphericpressure would thus be introduced into the equilibrium chamber. Inparallel with this, the pressure waveform is corrected, thus resultingin elimination of the unnecessary harmonic component. Fluctuations ofpressure in the equilibrium chamber therefore change into smoothbehavior like a sine wave, hence permitting control of fluctuations ofliquid pressure in the main liquid chamber in response to vibration ofthe vibrating body.

This is particularly effective when the length L1 of the duct line fromthe open air inlet to the equilibrium chamber cannot be set within theforegoing range. According to the present invention, an expansionchamber having a diameter larger than that of the duct line is providedbetween the open air inlet and the switching means and the length L2 ofthe duct line from the expansion chamber to the equilibrium chamber isset at a value determined by the following formula:

0.85cT/4≦L 2≦1.15cT/4

where c is the sound velocity (340 m/sec) and T is a period of time (inseconds) during which the open air is introduced into the equilibriumchamber by the switching means. By only appropriately adjusting thelength L2 of the duct line from the expansion chamber to the equilibriumchamber, therefore, the effect substantially the same as above isavailable. Therefore, when the length L1 of the duct line from the openair inlet to the equilibrium chamber cannot be set within the aboverange because of a particular necessity in piping, it suffices toprovide an expansion chamber having a length L2 satisfying the aboveformula.

In addition, in the vibration isolating apparatus of the presentinvention, the required frequency is the one required for synchronizingwith an idling vibration of the engine.

Further, the liquid-sealing type vibration isolating apparatus forachieving another object of the present invention comprises a mainchamber having a wall thereof formed by a part of the insulator andreceiving vibration directly propagating from the insulator, anauxiliary chamber connected to the main chamber via a small-diameterorifice so as to allow the liquid to flow and separated by a firstpartition plate comprising a rigid body from the main chamber, and anequilibrium chamber formed via a diaphragm between the main chamber andthe first partition plate and receiving any one of a negative pressureand the atmospheric pressure; and the liquid-sealing type vibrationisolating apparatus further comprising a second partition plate servingalso as a stopper, provided in the main chamber above the diaphragmforming the equilibrium chamber, a second orifice comprising alarge-diameter orifice in a portion of the second partition plate,switching means for performing a switching operation so as toalternately introduce any one of the negative pressure and theatmospheric pressure into the equilibrium chamber, in synchronizationwith engine vibration, and control means for controlling the switchingoperation of the switching means.

This constitution provides the following functions. First, as to idlingvibration, the negative pressure and the atmospheric pressure arealternately introduced at a specific frequency into the equilibriumchamber provided under the main chamber by operating the switchingmeans. That is, the pressure (volume) in the equilibrium chamber isaltered by ON/OFF-operating the switching means, thereby absorbingfluctuations of liquid pressure in the main chamber caused byidling-vibration entered via the insulator. This reduces the dynamicspring constant of the spring system formed by the insulator and thevibration isolating mechanism. This permits absorption and isolation ofidling vibration.

As to engine shake which is vibration of a frequency further lower thanthat of idling vibration, the liquid is caused to flow through thesmall-diameter orifice connecting the main chamber and the auxiliarychamber, thereby absorbing and isolating engine shake. Morespecifically, because engine shake vibration has a frequency of about 10Hz, it is difficult to isolate vibration by reducing the dynamic springconstant. In the present invention, therefore, the volume of theequilibrium chamber is kept null by continuously introducing a certainnegative pressure into the equilibrium chamber forming the vibrationisolating mechanism. This allows the liquid to flow through thesmall-diameter orifice formed between the main chamber and the auxiliarychamber, thereby causing generation of a prescribed damping force underthe effect of viscous drag resulting from the flow of the liquid. Engineshake is thus damped by the action of this damping force.

On the other hand, with respect to the vibration of a high frequency ofabout 100 to 600 Hz which causes a dull sound during travel of avehicle, the switching means is operated to bring the equilibriumchamber into the state open to the open air. The volume in the chambercan thus freely change in response to vibration of a frequency enteredvia the insulator and the liquid in the main chamber. The liquid in themain chamber is allowed to freely flow through the large-diameterorifice (second orifice) of the second partition plate provided in themain chamber, thus reducing the dynamic spring.constant of the springsystem formed by the vibration isolating mechanism to a low level. Theisolating effect against vibration in the high-frequency region is thusimproved. In the present invention, as described above, multiple kindsof vibration can be absorbed and isolated under the effect of theequilibrium chamber capable of changing the inner volume thereof byoperating the switching means comprising a switching valve or the like.

In the present invention, the second partition plate comprising a rigidbody is provided above the diaphragm forming the equilibrium chamber inthe main chamber. When vibration entered from the vibrating body has alarge amplitude, the downward stroke of the upper coupling member causedby this vibration from the vibrating body is arrested at this secondpartition plate. In other words, the second partition plate serves as aninner stopper of this vibration isolating apparatus. Under the effect ofthis stopper function, the diaphragm forming the equilibrium chamber isprotected upon input of vibration. As a result, the change in volume ofthe equilibrium chamber is kept normal, thus permitting reduction of thedynamic spring constant.

In the liquid-sealing type vibration isolating apparatus for achievingfurther another object of the present invention, the vibration isolatingmechanism comprises a liquid chamber sealing an incompressible fluid, anequilibrium chamber receiving a negative pressure or the atmosphericpressure, and an elastic diaphragm partitioning the liquid chamber andthe equilibrium chamber; a plurality of said vibration isolatingmechanisms are provided; a first liquid chamber provided in a firstliquid chamber provided in a first vibration isolating mechanism fromamong these plurality of vibration isolating mechanisms and a secondliquid chamber provided in a second vibration isolating mechanism areconnected with a large-diameter orifice; the first liquid chamberprovided in the first vibration isolating mechanism and a third liquidchamber provided in a third vibration isolating mechanism are connectedwith a small-diameter orifice; any one of a negative pressure and theatmospheric pressure is continuously introduced into a first equilibriumchamber provided in the first vibration isolating mechanism viaswitching means alternately in synchronization with engine vibration;and any one of a negative pressure and the atmospheric pressure iscontinuously introduced into a second equilibrium chamber provided inthe second vibration isolating mechanism in compliance with a switchingoperation of the switching means in response to the traveling state ofthe vehicle.

By adopting the foregoing constitution, the following effects areavailable in the present invention. Vibration from the vibrating body istransmitted via the coupling member to the insulator made of a rubbermaterial or the like. The insulator vibrates or deforms as a result andabsorbs or isolates most of the entered vibration. While most of thevibration is thus isolated at the insulator, a part thereof is notisolated at the insulator, but is isolated at the vibration isolatingmechanism following the insulator. Now, detailed operations of theindividual vibration isolating mechanisms will be described below.First, the vibration isolating function against engine idling vibrationwill be described. In this case, the frequencies to be covered rangefrom about 20 to 40 Hz. A negative pressure is therefore introducedthrough the switching means into the second equilibrium chamber in FIG.1 to bring the volume of the second equilibrium chamber to null. Thatis, the diaphragm in the second vibration isolating mechanism is keptinoperable. In this state, a negative pressure and the atmosphericpressure are alternately introduced into the first equilibrium chamberof the first vibration isolating mechanism at a certain cycle(frequency). As a result, the liquid in the first liquid chamberprovided under the insulator is about to flow through the small-diameterorifice to the third liquid chamber. However, because the negativepressure or the atmospheric pressure is introduced into the firstequilibrium chamber so that the diaphragm is applied with vibration at afrequency higher than the liquid resonance frequency of the liquidpresent in the orifice, the liquid in the first liquid chamber does notflow toward the small-diameter orifice. The status of the liquidpressure in the first liquid chamber largely fluctuates, and the liquidin the first liquid chamber is vibrated in the same phase as the enteredvibration. This inhibits increase in the dynamic spring constant in thepresent vibration isolating apparatus. That is, reduction of the dynamicspring constant is successfully achieved.

As to engine shake which is vibration caused during travel of a vehicleand has a frequency further lower than the idling vibration, a negativepressure is introduced into the first equilibrium chamber to bring thevolume of the first equilibrium chamber to null. In other words, thediaphragm of the first vibration isolating mechanism is kept inoperable.In this state, when vibration is transmitted from a vibrating body suchas an engine to the upper coupling member, the liquid pressure in thefirst liquid chamber increases, and the liquid in the first liquidchamber flows through the large-diameter orifice to the second liquidchamber of the second vibration isolating mechanism. The flow of theliquid in the first liquid chamber through the large-diameter orificemakes it available a high damping property. As a result, vibration ofengine shake having a frequency of about 10 Hz is inhibited. Vibrationcaused upon engine cranking, or vibration of a large amplitude causedupon sudden start or sudden acceleration, which is vibration of a largeamplitude at a further lower frequency is inhibited under the effect ofthe small-diameter orifice. The small-diameter orifice causes the liquidin the first liquid chamber to flow to the third liquid chamber againstinput of an initial load caused upon installation on the vibrating body,to keep balance of inner pressure in the individual liquid chambers.

As to vibration within a high frequency region of from 100 to 600 Hz,which poses the problem of a dull sound in the vehicle room, theatmospheric pressure is introduced into the first equilibrium chamber ofthe first vibration isolating mechanism to bring the first equilibriumchamber into the state open to the open air. At the same time, anegative pressure is continuously introduced into the second equilibriumchamber forming the second vibration isolating mechanism to bring thevolume of the second equilibrium chamber to null. The vibrationtransmitted through the upper coupling member into the first liquidchamber consequently vibrates the liquid in the first liquid chamber.However, since the first equilibrium chamber constituting the firstvibration isolating mechanism is in the state open to the open air, thediaphragm provided there freely vibrates. As a result, increase in theliquid pressure in the first liquid chamber is avoided against theentered vibration within the high frequency region, thus reducing thedynamic spring constant of this vibration isolating apparatus as awhole. This isolates vibration within the high frequency region whichcauses a dull sound.

In the present invention, as described above, the first equilibriumchamber and the second equilibrium chamber are independently kept in anegative pressure state or the atmospheric pressure state, or a negativepressure and the atmospheric pressure are alternately introduced at aspecific cycle (frequency) into the first equilibrium chamber. As aresult, a low dynamic spring constant is available over a wide range offrequency regions ranging from low-frequency vibration mainly comprisingidling vibration to high-frequency vibration centering around the dullsound. Reduction of the dynamic spring constant thus permits isolationof idling vibration and vibration associated with the dull sound. Engineshake which is low-frequency vibration can be isolated (inhibited) byobtaining a high damping property.

In the vibration isolating apparatus of the above constitution of thepresent invention, the housing space is a side branch having a closedend. Therefore, the vibration isolating apparatus is surely providedaccording to the above constitution.

Furthermore, the vibration isolating apparatus of the present inventionin another embodiment comprises a coupler attached to a vibrating body;a holder attached to the vehicle body side; an insulator providedbetween the coupler and the holder to absorb vibration from thevibrating body; a vibration isolator having a vibration isolatingmechanism directly following the insulator and comprising a main liquidchamber having a wall thereof formed by a part of the insulator andsealing a liquid therein, an auxiliary liquid chamber connected to themain liquid chamber so as to cause the liquid to flow via an orifice,and an equilibrium chamber provided at a portion of the main liquidchamber via a diaphragm so as to change the volume thereof in thechamber; switching means performing a switching operation based on afrequency required for synchronizing with vibration of the vibratingbody so as to introduce alternately a negative pressure from a negativepressure source and the atmospheric pressure from an atmosphericpressure inlet to the equilibrium chamber; and control means forcontrolling the switching means; wherein: a resistance for slowing downthe introduction of the negative pressure or the atmospheric pressureinto the equilibrium chamber is provided in the middle of acommunicating path communicating between the switching means and theequilibrium chamber.

In the vibration isolating apparatus of the above configuration of thepresent invention, the housing space is a side branch having a closedend.

In the vibration isolating apparatus of the above configuration of thepresent invention, the effects substantially the same as those of theapparatus of the preceding configuration are available. A resistance isprovided in the middle of a communicating path communicating between theswitching means and the equilibrium chamber. The presence of thisresistance slows down the increasing and decreasing rates of thepressure in the equilibrium chamber. Fluctuations of pressure in theequilibrium chamber therefore exhibit a smooth behavior, thus permittingcontrol of fluctuations of the liquid pressure in the main liquidchamber in response to vibration of the vibrating body.

The liquid-sealing type vibration isolating apparatus of the presentinvention for achieving further another object thereof comprises anupper coupling member attached to a vibrating body; a lower couplingmember attached to a member or the like on the vehicle body side; aninsulator provided between the upper coupling member and the lowercoupling member to absorb and isolate vibration from the vibrating body;a main chamber having a wall thereof formed by a part of the insulatorand sealing a liquid; an auxiliary chamber connected to the main chambervia a first orifice and having a part of the wall thereof formed by afirst diaphragm; a third liquid chamber connected to the main chambervia a second orifice and formed so as to receive the liquid in the mainchamber; and an equilibrium chamber partitioned and formed by a seconddiaphragm having a higher spring constant than the first diaphragmrelative to the third liquid chamber and receiving any one of theatmospheric pressure and a negative pressure; the liquid-sealingvibration type isolating apparatus further comprises switching means forperforming a switching operation so as to alternately introduce any oneof the negative pressure and the atmospheric pressure into theequilibrium chamber, in synchronization with engine vibration; andcontrol means controlling the switching operation of the switchingmeans.

By adopting the constitution as described above, the following functionsare available in the present invention. As to idling vibration, anegative pressure and the atmospheric pressure are alternatelyintroduced at a specific frequency into the equilibrium chamber byoperating the switching means. More specifically, the pressure (volume)in the equilibrium chamber is altered by operating the switching meansat a specific frequency to absorb fluctuations of the liquid pressure inthe insulator and the main chamber caused by idling vibration enteredthrough the insulator. As a result, there occurs a decrease in thedynamic spring constant of the spring system formed by the insulator andthe vibration isolating mechanism. Particularly in the apparatus of thepresent invention, operation of the second diaphragm causes the secondorifice having a prescribed volume to connect the third liquid chambersubjected to pressure fluctuations and the main chamber, and the liquidin the second orifice resonates with fluctuations of the liquid pressureof the liquid in the main chamber under the effect of operation of theequilibrium chamber, i.e., operation of the second diaphragm. Changes inthe power generated (vibrating energy) for the entire vibrationisolating mechanism are in a state of sine wave not containinghigh-frequency component noise, and this ensures absorption andisolation of idling vibration. It is also possible to avoid occurrenceof high-frequency vibration which may accompany the isolation of idlingvibration.

Regarding engine shake which is vibration of a frequency further lowerthan idling vibration, the liquid is caused to flow in the first orificeconnecting the main chamber and the auxiliary chamber, thereby absorbingand isolating engine shake. More specifically, when vibration of engineshake is entered (vibration input) into the main chamber, the liquid inthe main chamber receives pressure and acts to move the second diaphragmdownward through the second orifice and the third liquid chamber.However, the second diaphragm forming the equilibrium chamber has becomeharder to deform with a higher spring constant than the first diaphragmforming part of the auxiliary chamber. Upon input of engine shake intothe main chamber, therefore, the liquid in the main chamber flowsthrough the first orifice toward the auxiliary chamber side prior to thedeformation of the second diaphragm and to the volume change of theequilibrium chamber partitioned and formed by the second diaphragm. Ahigh damping property (high damping force) is available from the flowingmotion of the liquid in the first orifice, thereby inhibiting (damping)engine shake.

In the liquid-sealing type vibration isolating apparatus of the presentinvention as described above, a hardly deformable structure is adoptedas a whole for the second diaphragm forming the equilibrium chamber.That is, in the liquid-sealing type vibration isolating apparatus, thesecond diaphragm has a constitution having stopper-like projectionsalways in contact with both the partition plate forming the lowersurface of the equilibrium chamber and the plate partitioning the mainchamber and the third liquid chamber, these projections being arrangedon the upper and lower sides near the center of the diaphragm. Byadopting the constitution as described above, in the present invention,idling vibration is coped with by introducing any one of a negativepressure and the atmospheric pressure at a prescribed cycle into theequilibrium chamber through operation of the switching means. As aresult, the second diaphragm deforms (displaces) under the effect ofelastic deformation of the flat portion not containing projections,thereby vibrating the liquid in the third liquid chamber provided abovethe second diaphragm. This causes the vibrating force to propagatethrough the second orifice into the main chamber and acts to inhibit theincrease in the liquid pressure in the main chamber. Reduction of thedynamic spring constant for the entire vibration isolating apparatus isthus accomplished upon input of idling vibration.

Engine shake is on the other hand coped with by bringing the equilibriumchamber into the state open to the open air through operation of theswitching means. When engine shake is entered into the main chamber inthis state, fluctuations of the liquid pressure in the main chamber aretransmitted through the second orifice and the third liquid chamber tothe second diaphragm in response thereto. The deformation region of thesecond diaphragm itself has however become narrower because of thepresence of the projections, thus making it harder to deform (displace).The liquid in the main chamber therefore flows through the first orificetoward the auxiliary chamber having the wall thereof formed by theeasily deformable first diaphragm. A high damping property (high dampingforce) of the vibration isolating apparatus is available from thisflowing motion of the liquid to the first orifice. This high dampingforce inhibits (damps) the engine shake.

In the liquid-sealing type vibration isolating apparatus of theconstitution described above, the construction around the seconddiaphragm partitioning the third liquid chamber from the equilibriumchamber comprises a rubber-film-like diaphragm, and a spring serving toalways push back the rubber-film-like diaphragm toward the third liquidchamber. By adopting this constitution in the apparatus of the presentinvention, as in the preceding constitution, against idling vibration,an engine negative pressure and the atmospheric pressure are alternatelyintroduced into the equilibrium chamber by operating the switchingmeans, thereby causing the second diaphragm to deform in the stateresisting to the spring reaction force and eventually preventing theliquid pressure in the main chamber from increasing. As a result, thedynamic spring constant for the vibration isolating apparatus as a wholeis reduced upon input of idling vibration, thus permitting isolation ofidling vibration.

To cope with engine shake, the pressure transmitted through the secondorifice and the third liquid chamber to the second diaphragm is receivedwith the spring reaction of the spring so as not to cause deformation(displacement) of the second diaphragm. As a result, the liquid in themain chamber flows through the first orifice toward the auxiliarychamber having the wall partially formed by the easily deformable firstdiaphragm. A high damping property is available from the flowing motionof the liquid in the main chamber into the first orifice, thuseventually accomplishing damping (inhibition) the engine shake.

Another liquid-sealing type vibration isolating apparatus of the presentinvention is characterized in that the vibration isolating mechanism isin a cylindrical shape. More specifically, the apparatus comprises aninner cylinder forming a coupler attached to a vibrating body and havinga cylindrical shape; an outer cylinder forming a holder attached to thevehicle body side and having a cylindrical shape; an insulator providedaround the inner cylinder between the inner cylinder and the outercylinder; and a vibration isolating mechanism provided around theinsulator and sealing a liquid which is an incompressible fluid; thevibration isolating mechanism comprising a main chamber having a wallthereof formed by a part of the insulator; an auxiliary chamberconnected to the main chamber so as to allow the liquid to flow via,anorifice and separated from the main chamber by a partition platecomprising a rigid body; an equilibrium chamber provided at a part ofthe main chamber via a diaphragm and formed so that the volume thereofin the chamber changes; and an air chamber provided outside theauxiliary chamber via another diaphragm and constantly receiving air;the cylindrical liquid-sealing type vibration isolating apparatusfurther comprising switching means performing a switching operation soas to cause continuous and alternate introduction of any one of anegative pressure and the atmospheric pressure in synchronization withengine vibration, and control means for controlling the switchingoperation of the switching means. By adopting this constitution of thepresent invention, it is possible to achieve further downsizing andreduction of weight, and to save the space for supporting the vibratingbody.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view illustrating an engine mount and the like inaccordance with an embodiment of the present invention

FIG. 2 is a timing chart illustrating the behavior of a VSV and pressurein an equilibrium chamber with respect to the lapse of time inaccordance with an embodiment of the pent invention;

FIG. 3 is a longitudinal sectional view illustrating a wholeconfiguration of a vibration isolating mechanism in accordance withanother embodiment of the present inventions

FIG. 4 is a longitudinal sectional view illustrating a wholeconfiguration of a vibration isolating mechanism in accordance withfurther another embodiment of the present invention;

FIG. 5 is a graph showing changes in dynamic spring constant andcoefficient formed by selecting a diameter and a length of an orifice;

FIG. 6 is a sectional view illustrating a whole constitution of acylindrical liquid-sealing type vibration isolating apparatus inaccordance with another embodiment of the present invention;

FIG. 7 is a sectional view illustrating an engine mount and the like inaccordance with further another embodiment of the present invention;

FIG. 8 is a timing chart illustrating the behavior or a VSV and pressurein an equilibrium chamber with the lapse of time in accordance withanother embodiment of the present invention;

FIG. 9 is a partially enlarged sectional view illustrating furtheranother embodiment of the present invention;

FIG. 10 is a longitudinal sectional view illustrating a liquid-sealingtype vibration isolating apparatus in accords with another embodiment ofthe present invention;

FIG. 11 is a longitudinal sectional view illustrating a liquid-sealingtype vibration isolating apparatus in accordance with further anotherembodiment of the present invention;

FIG. 12 is a partially enlarged sectional view of a pressure controlportion provided in the apparatus of FIG. 1; and

FIG. 13 is a partially enlarged sectional view of a pressure controlportion provided in the apparatus of FIG. 7.

FIG. 14 is a timing chart illustrating the behavior of a VSV andpressure in an equilibrium chamber and an air chamber with respect tothe lapse of time in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, an embodiment of the present invention will be described withreference to the drawings. An engine as a vibrating body is mounted viaa plurality of engine mounts shown 3 on a vehicle body. The engine mountprovided on the rear side is of the liquid-sealing type conventionallyused in general, of which a detailed description is therefore omittedhere. The engine mount 3 provided on the front side is of theliquid-sealing type and has a configuration permitting alternateintroduction of a negative pressure and the atmospheric pressure, whichwill be described in detail later.

The engine has a plurality of combustion chambers (V-type 6 cylinders inthe present embodiment), and air is sucked and introduced through an aircleaner and an air inlet path into each combustion chamber. A throttlevalve is provided in the middle of the air inlet path, and the flow rateof sucked air flowing through the air inlet path is adjusted byopening/closing this throttle valve. A fuel injecting valve not shown isprovided in a port immediately preceding the combustion chamber of theair inlet path. A combustible mixed gas is formed by a fuel injectedfrom this injecting valve and the aforesaid sucked air and introducedinto the combustion chamber. As the configuration itself of an engine isconventionally known, a further description thereof is omitted here.

Now, the construction of the foregoing engine mount 3 will be describedbelow. As shown in FIG. 1, the engine mount 3 has a coupler 11 as afitting attached to the engine 1, a holder 12 attached to the vehiclebody side, an insulator 13 provided between the coupler 11 and theholder 12 for mainly absorbing vibration transmitted from the engine 1,and a vibration isolating mechanism 14 provided immediately followingthe insulator 13. The insulator 13 is made of a vibration-proof rubbermaterial and connected integrally to the coupler 11 by vulcanizationbonding or the like. The vibration isolating mechanism 14 has a wallthereof formed by a part of the insulator 13 and comprises therein amain liquid chamber 15 sealing a liquid therein, an auxiliary liquidchamber 17 connected to the main liquid chamber 15 via an orifice 16 toallow the liquid to flow, an equilibrium chamber 19 provided in aportion of the main liquid chamber 15 via a first diaphragm 18 andformed so as to permit a change in the volume thereof, and an airchamber 21 provided around (under) the auxiliary liquid chamber 17 via asecond diaphragm 20 and always receiving introduced air. The main liquidchamber 15 and the auxiliary liquid chamber 17 are separated by apartition plate 22.

A communicating path 23 is provided in the equilibrium chamber 19, andan end of this communicating path 23 communicates with a vacuumswitching valve (VSV) 31 forming switching means 25 in a pressurecontrol portion as encircled with a dashed line in FIG. 1. The VSV 31is, for example, a three-way valve ON/OFF-switched over by a solenoid32, and has first, second and third ports 33, 34 and 35. The first port33 communicates through the communicating path 23 with the equilibriumchamber 19, as described above. As shown in FIG. 1, the second port 34communicates with the air inlet path in the upstream of the throttlevalve via an atmospheric pressure duct line 35. The third port 35communicates with the air inlet path in the downstream of the throttlevalve (surge tank) via a negative pressure duct line 37. A vacuum tankas a negative pressure source is provided in the middle of the negativepressure duct line 37 to permit constant storage of a negative pressuregenerated in the downstream of the throttle valve.

The VSV is controlled by a central processing unit (CPU) 41 as controlmeans. This CPU issues a signal to the effect of ON/OFF switching overthe VSV 31 at intervals of, for example, a predetermined period. Whenthe CPU 41 gives an output of an ON signal, the first port 33 and thesecond port 34 are brought into the communicating state, and sucked air(atmospheric pressure) in the upstream of a throttle valve 7 isintroduced into the equilibrium chamber 19. When an OFF signal is issuedby the CPU 41, on the other hand, the first port 33 and the third port35 are brought in to the communicating state, and sucked air (negativepressure) generated in the down-stream of the throttle valve 7 andstored in the vacuum tank 38 is introduced into the equilibrium chamber19. In this embodiment, the vibration isolating apparatus is composed ofthe above-mentioned engine mount 3, the VSV 31 and the CPU 41.

Now, the features of this embodiment will be described. In thisembodiment, a box-shaped expansion chamber 51 having a larger diameterthan that of the atmospheric pressure duct line 36 is provided in themiddle of the duct line 36. The positional relationship of the expansionchamber 51 is important in this embodiment. More specifically, uponintroduction of the open air through the atmospheric pressure duct line36 into the equilibrium chamber 19, pulsation is caused in the suckedair, and the frequency of this pulsation is determined by the length L2of the duct line between the equilibrium chamber 19 and the expansionchamber 51. In this embodiment, the length L2 is set so as to satisfythe following formula:

0.85c/4f≦L 2≦1.15c/4f

where, c is the sound velocity (340 m/sec) and f is the requiredfrequency (for example, the one corresponding to the idlingfrequency)[Hz].

Then, operations and effects of this embodiment having the configurationas described above will be described below.

In the present embodiment, most of the vibration transmitted from theengine 1 is absorbed by the insulator 13. Vibration is furthercontrolled and absorbed by the vibration isolating mechanism 14immediately following the insulator 13. That is, the liquid sealed inthe main liquid chamber 15 and the auxiliary chamber 17 flows throughthe orifice 16 as a result of vibration, and the vibration is controlledand absorbed by this flow.

Along with this, a negative pressure from the vacuum tank and thenegative pressure duct line 37 and the atmospheric pressure from theatmospheric pressure duct line 36 are alternately introduced into theequilibrium chamber 19 provided via the first diaphragm 18 in a portionof the main liquid chamber 15. This introduction is accomplished byswitching of the VSV 31 controlled by the CPU 41 on the basis of therequired frequency (for example, the one corresponding to the idlingfrequency) f. This switching permits alternate introduction of thenegative pressure and the atmospheric pressure at a frequencycorresponding to the required frequency f, and the pressure and hencethe volume of the equilibrium chamber 19 change in response to thisintroduction. Such a change in the volume positively controls andabsorbs fluctuations of the liquid pressure in the main liquid chamber15, produced by the engine 1 vibration and entered through the insulator13.

Because the VSV 31 is to be changed over by switching, a harmoniccomponent may be produced along with this switching. To avoid thisinconvenience, in this embodiment, the length L2 between the equilibriumchamber 19 and the expansion chamber 51 is set at a value determined bythe foregoing formula. Pulsation is therefore produced in air introducedfrom the atmospheric pressure duct line 36, thus temporarily bringingabout an inertial supercharging state. As shown in FIG. 2, a pressurehigher than the atmospheric pressure would therefore be introduced intothe equilibrium chamber 19.

At the same time, a pressure waveform is corrected, and this wouldeventually eliminate the unnecessary harmonic component. The pressure inthe equilibrium chamber 19 therefore exhibits a smooth behavior like asine wave, thus permitting control of fluctuations of liquid pressure inthe main liquid chamber 15 in agreement with vibration of the engine 1.The driver of the vehicle can consequently inhibit more certainly thevibration generated from the engine from propagating into the vehicleroom.

According to the present embodiment, the expansion chamber 51 isprovided in the middle of the atmospheric pressure duct line 36.Propagation of vibration into the vehicle room is inhibited by settingthe length L2 between the equilibrium chamber 19 and the expansionchamber 51 at a value satisfying the foregoing formula. The same effectsas those described above are substantially available only byappropriately adjusting the length L2 of the duct line between theexpansion chamber 51 and the equilibrium chamber 19. Therefore, evenwhen an arbitrary length of the atmospheric pressure duct line 36 cannotbe set for piping convenience of the duct line, it is possible toinhibit propagation of vibration without fail.

In the present embodiment, furthermore, the present invention isapplicable to a case where an engine mounted on a vehicle body is thevibrating body. It is therefore possible to effectively control andabsorb vibration generated by the engine.

In addition, according to this embodiment, the negative pressure sourceshould be based on a negative pressure produced in the downstream of thethrottle valve provided in the middle of the air intake path of theengine. It is therefore possible to utilize an air intake system of anordinary engine, thus eliminating the necessity of a separate negativepressure source, and permitting inhibition of the increase in cost.

Further, according to this embodiment, the required frequency f issynchronized with the idling vibration. It is therefore possible toeffectively control and absorb the idling vibration of the engine.

Application of the present invention is not limited to the above, butthe details may be modified as follows.

(1) While the expansion chamber 51 has been provided in the middle ofthe atmospheric pressure duct line 36 in the foregoing embodiment, aconstitution without an expansion chamber 51 may be adopted. In thiscase, the length L1 of the duct line between the atmospheric pressureinlet and the equilibrium 19 should take a value determined by thefollowing formula:

0.85cT/4≦L 1≦1.15cT/4

(where, c is the sound velocity [340 m/sec], and T is the period of time[in seconds] during which the open air is introduced through the VSV 31into the equilibrium chamber 19), and:

0.85c/4f≦L 2≦1.15c/4f.

And, in this embodiment, as shown in the embodiment of FIG. 7, thecommunication path 23 may provide with a side branch, and as shown inthe embodiment of FIG. 9, the communication path 23 may provide with aresistance portion. Then, the expansion chamber 51 may be used togetherwith the side branch.

Now, another embodiment of the present invention will be describedbelow. The basic constitution of this embodiment comprises, as shown inFIG. 3, an upper coupling member, i.e., a coupler 11, attached to avibrating body, a lower coupling member, i.e., a holder 12, attached toa member or the like on the vehicle body side, an insulator 13 providedbetween the upper coupling member 11 and the lower coupling member 12for absorbing and isolating vibration from a vibrating body, liquidchambers 111 and 17 sealing a liquid which is an incompressible fluid,provided in series with the insulator 13, and a vibration isolatingmechanism 14 formed by an air chamber 21 provided via a diaphragm 20below these liquid chambers.

In this basic constitution, the aforesaid vibration isolating mechanism14 comprises a main chamber 111 comprising a liquid chamber having awall thereof formed by a part of the foregoing insulator 13, receivingvibration directly from the insulator 13, an auxiliary chamber 17connected to the main chamber 111 via a small-diameter orifice 16 so asto cause the liquid to flow and separated from the main chamber 111 witha first partition plate 39, and an equilibrium chamber 19 formed betweenthe main chamber 111 and the first partition plate 39 via a diaphragm18, into which any one of a negative pressure and the atmosphericpressure is introduced. In this constitution, a second partition plate44 serving also as a stopper is provided above a diaphragm 18 formingthe equilibrium chamber 19 in the main chamber 111, and further, asecond orifice 4 comprising a large-diameter orifice having a largeopening area is provided in a portion of the second partition plate 44.In addition, any one of a negative pressure and the atmospheric pressureis continuously or alternately introduced into the equilibrium chamber19. Switching means 25 conducting switching operation so as toalternately introduce the negative pressure and the atmospheric pressureinto the equilibrium chamber 19 comprises a switching valve 31comprising a three-way valve or the like, and a solenoid 32 for drivingthe switching valve 31. A throttle valve 29 as shown in FIG. 3 can beprovided on the atmospheric pressure introducing port side of theswitching valve 31 with a view to balancing the introducing rate of theatmospheric pressure with the introducing rate of the negative pressureinto the equilibrium chamber 19. In this constitution, furthermore,control means 41 for controlling operation of the solenoid 32 of theswitching means 25 is provided in a pressure control portion asencircled with a dush line in FIG. 3. This control means 41 is composedof a microcomputer comprising computing means mainly including amicroprocessor unit (MPU).

Now, operations of the apparatus in this embodiment will be describedbelow. First, as to idling vibration, a negative pressure and theatmospheric pressure are alternately introduced at a specific frequencyinto the equilibrium chamber 19 provided below the main chamber 111 byoperating the switching means 25. More particularly, the pressure(volume) of the equilibrium chamber 19 is altered by ON/OFF-operatingthe switching means 25, thereby absorbing fluctuations of the liquidpressure in the main chamber 111 caused by idling vibration entered viathe insulator 13. As a result, the dynamic spring constant of the springsystem formed by the insulator 13 and the vibration isolating mechanismis reduced, thus permitting absorption and isolation of the idlingvibration.

As to engine shake which is vibration of a further lower frequency thanthe idling vibration, the liquid is allowed to flow through an orifice(small-diameter orifice) connecting the main chamber 111 and theauxiliary chamber 17, thereby absorbing and isolating engine shake.Since engine shake vibration has a frequency of about 10 Hz, it isdifficult to isolate vibration by reducing the dynamic spring constant.In this embodiment, therefore, a certain negative pressure iscontinuously introduced into the equilibrium chamber 19 forming thevibration isolating mechanism 14 to keep the volume of the equilibriumchamber 19 in null. This causes the liquid to flow through thesmall-diameter orifice 5 formed between the main chamber 111 and theauxiliary chamber 17 to obtain a prescribed damping force by means ofthe viscous drag resulting from this flow of the liquid. The engineshake is damped by this damping force.

As to vibration of a high frequency within a range of from 100 to 600 Hzwhich causes a dull sound posing a problem during travel of a vehicle,the equilibrium chamber 19 is brought into the state open to the openair by operating the switching means 25, whereby the inner volume of theequilibrium chamber 19 can freely vary relative to vibration of afrequency within the aforesaid range, entered via the liquid in theinsulator 13 and the main chamber 111. As a result, the liquid in themain chamber 111 freely flows through the large-diameter orifice 4 ofthe second partition plate 44 provided in the main chamber 111, thusreducing the dynamic spring constant of the spring system formed by thevibration isolating mechanism. Isolation of high-frequency vibration isthus accomplished in response to the opening area of the orifice 4. Inthe apparatus of this embodiment, therefore, a plurality of kinds ofvibration can be absorbed and isolated under the effect of theequilibrium chamber 19 having a varying inner volume by operating theswitching means 25.

In the apparatus of this embodiment, furthermore, as shown in FIG. 3, asecond partition plate 44 comprising a rigid body is provided above thediaphragm 18 forming the equilibrium chamber 19 in the main chamber 111.Under the effect of this second partition plate 44, therefore, when anentered vibration from the vibrating body has a large amplitude, afurther downward stroke of the upper coupling member 6 brought about bythe input of vibration from the vibrating body is arrested at the secondpartition plate. More specifically, the second partition plate 44 servesalso as an inner stopper of the vibration isolating mechanism. Under theeffect of this stopper function, the diaphragm 18 forming theequilibrium chamber 19 is protected upon input of vibration. As aresult, the inner volume of the equilibrium chamber 19 normally varies,thereby ensuring reduction of the dynamic spring constant.

In this embodiment, the communication path 23 to the equilibrium chamber19 may provide with a side branch or a resistance portion, and theatmospheric pressure duct line 36 may provide with an expansion chamber.Then, the expansion chamber may be used together with the side branch.

Now, further another embodiment of the present invention will bedescribed below with reference to FIGS. 4 and 5. The present embodimentdiffers from that described with reference to FIG. 3 in that threevibration isolating mechanisms are provided, and has a basicconfiguration, as shown in FIG. 4, comprising an upper coupling member11 attached to a vibrating body, a lower coupling member 12 attached toa member or the like on the vehicle body side, an insulator 13 providedbetween the upper coupling member 11 and the lower coupling member 12for absorbing and isolating vibration from the vibrating body, andvibration isolating mechanisms 1, 2 and 3 provided in series with theinsulator 13 and formed by a liquid chamber sealing a liquid which is anincompressible fluid, and the like. In this basic configuration, thepresent embodiment is provided with three vibration isolatingmechanisms. A first vibration isolating mechanism 1 comprises a firstliquid chamber 11 formed below the insulator 13, into which vibrationfrom the vibrating body is entered via the insulator 13, a firstequilibrium chamber 46, formed below the first liquid chamber 11, intowhich a negative pressure and the atmospheric pressure are alternatelyintroduced at a prescribed cycle (frequency), and an elastic film-shapeddiaphragm 45 partitioning the first liquid chamber 11 and the firstequilibrium chamber 46. A second vibration isolating mechanism 2provided below the first vibration isolating mechanism 1 comprises asecond liquid chamber 47 connected to the first liquid chamber 11 of thefirst vibration isolating mechanism 1 via a large-diameter orifice 4, asecond equilibrium chamber 19, provided below the second liquid chamber47, into which a negative pressure or the atmospheric pressure iscontinuously introduced, and a diaphragm 18 partitioning the secondliquid chamber 47 and the second equilibrium chamber 19. A thirdvibration isolating mechanism 3 comprises a third liquid chamber 17connected to the first liquid chamber 11 provided in the first vibrationisolating mechanism 1 via a small-diameter orifice 5, a thirdequilibrium chamber 21, provided below the third liquid chamber 17,comprising an air chamber always receiving the introduced atmosphericpressure, and a film-shaped diaphragm 20 partitioning the third liquidchamber 17 and the third equilibrium chamber (air chamber) 21.

In this constitution, the individual vibration isolating mechanisms 1, 2and 3 are separated by partition members 44 and 39 as shown in FIG. 4,integrally gathered with the insulator 13 and the like, and arrangedbetween the upper coupling member 11 and the lower coupling member 12 toform a liquid-sealing type vibration isolating apparatus. In thisconfiguration, a negative pressure or the atmospheric pressure isintroduced through a first switching means 55 into the first equilibriumchamber 45 of the first equilibrium chamber 46 of the first vibrationisolating mechanism 1. In the pressure control portion as encircled witha dashed line in FIG. 4, the first switching means 55 comprises aswitching valve 56 comprising a three-way valve or the like and asolenoid 57 operating the switching valve 56. The solenoid 57 controlsthe switching operation by means of control means 41 comprising amicrocomputer mainly consisting of computing means such as amicroprocessor unit (MPU). The solenoid 57 is thus driven on the basisof a control signal from the control means 41. An ON/OFF operation ofthe switching valve 56 maintains the first equilibrium chamber 46 in anyof a certain negative pressure state or the atmospheric pressure (opento the open air) state, or causes alternate introduction of the negativepressure and the atmospheric pressure at a prescribed cycle (frequency).When the negative pressure and the atmospheric pressure are alternatelyintroduced, a throttle valve 59 as shown in FIG. 1 is provided on theatmospheric pressure introducing port side of the switching valve 56 forbalancing the introducing rate of the atmospheric pressure and theintroducing rate of the negative pressure into the first equilibriumchamber 46.

A negative pressure or the atmospheric pressure is appropriatelyintroduced through the second switching means 25 at the secondequilibrium chamber 19 of the second vibration isolating mechanism 2.The second switching means 25 comprises a switching valve 31 comprisinga three-way valve or the like and a solenoid 32 for operating theswitching valve 31. The solenoid 32 controls the switching operation bymeans of the control means 41 comprising a microcomputer mainlyconsisting of computing means such as a microprocessor unit (MPU).Therefore, the second switching means 25 performs a switching operationon the basis of the control operation of the control means 41, and thesecond equilibrium chamber 19 is thus kept in a prescribed negativepressure state or the atmospheric pressure state.

Now, operations of the apparatus in the present embodiment comprisingthe constitution as described above will be described below. First, thevibration isolating operation against engine idling vibration is asfollows. Covered frequencies in this case range from about 20 to 40 Hz.A negative pressure is therefore introduced through the second switchingmeans 25 into the second equilibrium chamber 19 in FIG. 4 to bring thevolume of the second equilibrium chamber 19 to null. That is, theoperation of the diaphragm 18 in the second vibration isolatingmechanism is prevented. In this state, the negative pressure and theatmospheric pressure are alternately introduced at a prescribed cycle(frequency) into the first equilibrium chamber 46 of the first vibrationisolating mechanism 1. As a result, the liquid in the first liquidchamber 11 provided below the insulator 13 tends to flow toward thethird liquid chamber 17 through the small-diameter orifice 5. However,because the diaphragm 45 forming the first equilibrium chamber 46 isvibrated at a frequency higher than the resonance frequency of theliquid present in the small-diameter orifice 5, and this causesfluctuations of volume of the first equilibrium chamber 46, the liquidin the first liquid chamber 11 cannot flow through the small-diameterorifice. As a result, the liquid pressure in the first liquid chamber 11is caused to largely vary, and the liquid in the first liquid chamber 11vibrates in phase state in which the increase in the liquid pressure inthe first liquid chamber 11 caused by input vibration is canceled. Thedynamic spring constant formed in the first vibration isolatingmechanism 1 and the like is thus reduced.

As to engine shake which is vibration of a frequency further lower thanthe idling vibration described above, produced during travel of thevehicle, a negative pressure is introduced into the first equilibriumchamber 46 to bring the volume of the first equilibrium chamber 46 tonull. That is, the diaphragm 45 in the first vibration isolatingmechanism 1 is kept inoperable. When vibration is transmitted from thevibrating body such as an engine to the upper coupling member 11 in thisstate, the liquid pressure in the first liquid chamber 11 increases, andthe liquid in the first liquid chamber 11 flows through thelarge-diameter orifice 4 into the second liquid chamber 47 of the secondvibration isolating mechanism 2. A high damping property is availablefrom the flow of the liquid in the first liquid chamber 11 through thelarge-diameter orifice 4. Vibration associated with engine shake havinga frequency of about 10 Hz is consequently inhibited. By making thesmall-diameter orifice 5 capable of coping with vibration of a lowerfrequency under 5 Hz than engine shake, it is possible to inhibit suchlarge-amplitude vibration as vibration upon engine cranking with a lowfrequency and a large amplitude, and vibration of a large amplitudeproduced upon sudden start or sudden acceleration, under the effect ofthe small-diameter orifice 5. The small-diameter orifice 5 causes theliquid in the first liquid chamber 11 toward the third liquid chamber 17upon input of an initial load during installation on the vibrating body,to take balance of the inner pressure in these liquid chambers 11 and17.

With regard to vibration within a high frequency region of from 100 to600 Hz, which poses a problem of a dull sound in the vehicle room, thefirst equilibrium chamber 46 in the first vibration isolating mechanismin FIG. 4 is brought into the state open to the open air. At the sametime, a negative pressure is continuously introduced into the secondequilibrium chamber 19 forming the second vibration isolating mechanism2 to bring the second equilibrium chamber 19 into the zero-volume state.The vibration transmitted through the upper coupling member 6 into thefirst liquid chamber 11 consequently vibrates the liquid in the firstliquid chamber 11. Since the first equilibrium chamber 46 forming thefirst vibration isolating mechanism 1 is in the state open to the openair, the diaphragm 45 provided therein can freely vibrate. As a result,increase in the liquid pressure in the first liquid chamber 11 can beavoided against the entered vibration of a frequency within the highfrequency region, and the dynamic spring constant is reduced for theentire vibration isolating apparatus. It is thus possible to isolatevibration within the high-frequency region which causes a dull sound.

According to the present embodiment, as described above, it is possibleto obtain a low dynamic constant over a wide range of frequenciesranging from vibration within the low-frequency region mainly includingidling vibration to vibration within the high-frequency region coveringa dull sound by keeping the first equilibrium chamber 46 and the secondequilibrium chamber 19 independently in a negative pressure state or inthe atmospheric pressure state, or alternately introducing a negativepressure or the atmospheric pressure at a specific cycle (frequency)into the first equilibrium chamber. By the reduction of the dynamicspring constant, idling vibration and vibration associated with dullsound can be isolated. It is also possible to isolate (inhibit) engineshake which is a low-frequency vibration by obtaining a high dampingproperty. The resonance action of the liquid present in the orifice 4and the second liquid chamber 47 and the dynamic spring constant formedat the insulator 13 constituting the main spring can be caused to agreewith a specific target frequency (f₁) as shown in FIG. 5 by bringing thefirst equilibrium chamber 46 in this state into the zero-volume stateand appropriately setting the diameter and length of the large-diameterorifice 4. This permits isolation of vibration having the specifictarget frequency (f₁).

In this embodiment, the communication paths to each the equilibriumchambers may provide with a side branch or a resistance portion, and theatmospheric pressure duct line may provide with an expansion chamber.Then, the expansion chamber may be used together with the side branch.

Another embodiment of the present invention will now be described belowwith reference to FIG. 6. The basic constitution in this embodimentcomprises, as shown in FIG. 6, an inner cylinder 77 forming a couplerattached to a vibrating body side, an outer cylinder 66, serving as aholder attached to the vehicle body side, to be attached to a bracket12, an insulator 13 provided between the inner cylinder 77 and the outercylinder 66 around the inner cylinder 77 connected to the vibratingbody, a vibration isolating mechanism 14, provided around the insulator13, and formed by a main chamber 15 and an auxiliary chamber 17 sealinga liquid which is an incompressible fluid, an equilibrium chamber 19,provided in the main chamber 15 of the vibration isolating mechanism 14,receiving a negative pressure or the atmospheric pressure, switchingmeans 25 performing a switching operation of the negative pressure orthe atmospheric pressure introduced into the equilibrium chamber 19, andcontrol means 41 controlling the switching operation of the switchingmeans 25.

In this basic constitution, the insulator 13 is made of avibration-proof rubber material and integrally bonded to the innercylinder through vulcanization adhering means. The vibration isolatingmechanism 14 comprising the main chamber 15 and.the like is providedaround the insulator 13 of this configuration. As shown in FIG. 6, thevibration isolating mechanism 14 basically comprises the main chamber 15following the insulator 13 and having a wall thereof formed by a part ofthe insulator 13, an auxiliary chamber 17 provided opposite to the mainchamber 15 and separated by a ring-shaped partition plate 22, an orifice16 connecting the main chamber 15 and the auxiliary chamber 17 andprovided along the inside of the outer cylinder 66, an air chamber 21provided via another diaphragm 20 outside the auxiliary chamber 17 andconstantly receiving air, and an equilibrium chamber 19 formed via adiaphragm 18 in a space. forming the main chamber 15.

In this basic constitution, the orifice 16 is provided between the mainchamber 15 and the auxiliary chamber 17, and the liquid flows betweenthe main chamber 15 and the auxiliary chamber 17. A stopper comprising arubber-like elastic body is arranged in the main chamber 15, and a rigidprotector 88 is provided below the stopper 8. When vibration of a largeamplitude is entered from the vibrating body, the diaphragm 18 formingthe equilibrium chamber 19 is protected by the stopper 8 and theprotector 88. The insulator 13 comprising such a configuration and thevibration isolating mechanism 14 formed centering around the insulator13 are installed in the outer cylinder 66, and the outer cylinder 66 isattached to a bracket 12 connected to a member or the like on thevehicle body side.

In the pressure control portion as encircled with a dashed line in FIG.6, a communicating path is provided at the equilibrium chamber 19forming the vibration isolating mechanism 14 comprising the aboveconfiguration, and an end of this communicating path 23 is connected toswitching valve 31 forming switching means 25. The switching valve 31comprises a three-way valve and causes the equilibrium chamber 19 tocommunicate with a negative pressure source or to the open air byappropriately switching over the valve. The switching operation of theswitching means 25 is accomplished by an integrally provided solenoid32. That is, the switching means 25 is formed by the solenoid valve. Athrottle valve 29 for balancing the introducing rate of the atmosphericpressure and the introducing rate of the negative pressure is providedon the atmospheric pressure introducing port side of the switching valve31 having the configuration described above.

The control means 41 controlling the switching operation of theswitching means 25 comprises a microcomputer (CPU) formed on the basisof a microprocessor unit. The switching means 25 is driven by thecontrol action of the control means 41 of this configuration, and thiscauses introduction of the negative pressure formed by a negativesuction pressure of the engine or the atmospheric pressure formed byopening to the open air into the equilibrium chamber 19. Introduction ofthe negative pressure or the atmospheric pressure via the switchingmeans 25 drives (deforms) the diaphragm 18 forming a portion of theequilibrium chamber 19, and absorbs fluctuations of the liquid pressuregenerated in the main chamber 15.

Now, operations of the apparatus of this embodiment having theconstitution described above will be described below. As shown in FIG.6, vibration from the vibrating body side is transmitted via the innercylinder 77 to the insulator 13 comprising a rubber material. As aresult, the insulator 13 vibrates or deforms, thus absorbing orisolating most of the entered vibration. Therefore, most of thevibration is isolated at the insulator 13, while a portion of vibrationis not isolated at the insulator 13, but is isolated at the followingvibration isolating mechanism 14. Now, detailed operations in thevibration isolating mechanism 14 will be described below. First, as toidling vibration, a negative pressure and the atmospheric pressure arealternately introduced at a specific frequency into the equilibriumchamber 19 provided in the main chamber 15 in the lower part thereof byoperating the switch means 25. In other words, the pressure (volume) inthe equilibrium chamber 19 is altered by operating the switching means25 at a specific frequency, thereby absorbing fluctuations of the liquidpressure in the main chamber 15 caused by idling vibration entered viathe insulator 13. As a result, the dynamic spring constant of the springsystem formed by the insulator 13 and the vibration isolating mechanism14 is reduced, thus accomplishing absorption and isolation of idlingvibration.

As to engine shake which is vibration of a frequency of about 10 Hz,lower than that of idling vibration, it is difficult to isolatevibration by reducing the dynamic spring constant. In the presentembodiment, therefore, vibration associated with engine shake isinhibited (damped) by improving damping property in the vibrationisolating mechanism 14. That is, a certain negative pressure isintroduced into the equilibrium chamber 19 forming the vibrationisolating mechanism 14 to bring the volume in the equilibrium chamber 19to null. As a result, the liquid flows through the orifice 16 formedbetween the main chamber 15 and the auxiliary chamber. 17, therebyproducing a certain damping force under the effect of viscous dragresulting from the flow of the liquid. This damping force permitsdamping of engine shake.

Regarding vibration of a high frequency within a range of from about 100to 600 Hz, which causes a dull sound, a problem during travel of thevehicle, on the other hand, the switching means 25 is operated tomaintain the equilibrium chamber 19 in the state open to the open air.The inner volume of the equilibrium chamber 19 can thus freely change inresponse to the vibration of the high frequency entered via the liquidin the insulator 13 and the main chamber 15. As a result, the liquid inthe insulator 13 and the main chamber 15 can freely vibrate, and it ispossible to inhibit the dynamic spring constant of the spring systemformed by the vibration isolating mechanism 14 to a low level, thusimproving the isolating effect relative to high-frequency vibration.

In further another embodiment of the present invention, the surfacestructure at the particular plate forming the equilibrium chamber may bemodified (variation). The partition plate has fine irregularities on thesurface so as to permit flow of air. These fine irregularities areformed by surface-treating the surface to roughen the same by theapplication of shot blasting means or craping means. A smooth layer isformed by applying a urethane-based paint or a silicone-based paint onthe contact side of the diaphragm in contact with the surface of thepartition plate.

By adopting the constitution mentioned above, when a negative pressureor the atmospheric pressure is introduced, and the vibrating diaphragmcomes into contact with the partition plate, the partition plate and thediaphragm never come into close contact. More specifically, innumerablemicrospically fine irregularities are provided on the surface of thepartition plate in contact with the diaphragm, and continuous groovesare formed between these fine irregularities. Therefore, even when thediaphragm is attracted by a negative pressure and comes into contactwith the surface of the partition plate having these fineirregularities, many gaps are formed between them. The grooves formed bythese gaps communicate with spaces other than those in which thediaphragm is present. The diaphragm therefore never comes into closecontact with, or is never attracted by, the surface of the partitionplate. As a result, the diaphragm smoothly operates (deforms) inresponse to introduction of the negative pressure or the atmosphericpressure from the switching means, thus permitting smooth progress ofthe change in the volume of the equilibrium chamber formed by thediaphragm.

In this embodiment, the atmospheric pressure duct line 51 may providewith an expansion chamber, and the communication path 23 may providewith a side branch or a resistance portion. Then, the expansion chambermay be used together with the side branch.

Another embodiment of the present invention shown in FIG. 7 will now bedescribed below. Because the present embodiment has the same basicconstitution as the embodiment of FIG. 1, only the features as shown inFIG. 13 will be described. In a pressure control portion of thisembodiment as encircled with a dashed line in FIG. 7, a side branch 51constituting a housing space is provided in the middle of thecommunicating path 23 communicating between the first port 33 of the VSV31 of the switching means 25. The side branch 51 is formed in a tubularshape (the diameter should preferably be over 2 mm) so as to branch fromthe communicating path 23 and has a closed tip end. In this embodiment,the length L of the side branch 51 is set so as to satisfy the followingformula:

0.85c/f≦L≦1.15c/4f

where c is the sound velocity [340 m/sec] and f is the frequency [Hz]corresponding to the harmonic component in the required frequency (forexample, in idling frequency).

The functions and effects of the embodiment having the constitutiondescribed above will be described. Since the VSV 31 of the switchingmeans 25 is switched over through switching operation, a harmoniccomponent may result from switching. In this embodiment, in contrast,the side branch 51 is provided in the communicating path 23. Pulsationcan therefore be produced in the atmospheric pressure and a negativepressure introduced from an atmospheric pressure duct line 36 and anegative pressure duct line 37. AS shown in FIG. 8, the resonance effectof the pulsation adjusts the pressure waveform, thus resulting inelimination of the unnecessary harmonic component. Presence of the sidebranch slows down the increasing and decreasing rates of pressure in theequilibrium chamber 19. Fluctuations of pressure in the equilibriumchamber 19 therefore exhibit a smooth behavior as a sine wave, therebypermitting control of fluctuations of pressure of the liquid in the mainliquid chamber 15 in response to vibration of the engine 1. As a result,the driver of the vehicle can more certainly inhibit propagation ofvibration from the engine into the vehicle room by means of thevibration isolating apparatus described above.

According to the present embodiment, it is possible to eliminate theharmonic component from the produced pulsation by setting a length L ofthe side branch 51 so as to satisfy the foregoing formula, thus ensuringmore certain achievement of the effects described above.

According to this embodiment, furthermore, the invention is applicableto a case where an engine 1 mounted on a vehicle body is the vibratingbody. It is possible to effectively control and absorb vibrationproduced in the engine 1.

In this embodiment, a negative pressure source based on a negativepressure produced in the downstream of a throttle valve 7 provided inthe middle of an intake path 6 of the engine 1 is employed. It istherefore possible to utilize an ordinary suction system of the engine1, thus eliminating the necessity of a separate negative pressuresource. As a result, increase in the cost can be inhibited.

In addition, according to this embodiment, the required frequency fshould be in synchronization with the idling vibration of the engine 1.It is therefore possible to effectively control and absorb particularlyidling vibration of the engine 1.

In this embodiment, as in the embodiment of FIG. 1, the atmosphericpressure duct line 36 may provide with an expansion chamber, and thecommunication path 23 as in the embodiment of FIG. 9 may provide with aresistant portion. Then, the expansion chamber may be used together withthe side branch 51.

Now, further another embodiment of the present invention will bedescribed below. Because the basic constitution of this embodiment isthe same as that of the above-mentioned embodiment of FIG. 7, the samereference numerals are assigned to the corresponding members and thedescription is omitted here. The following description will thereforecenter around the differences from the second embodiment.

In this embodiment, as shown in FIG. 9, a foaming body 52 is provided asa resistance having permeability in the middle of the communicating path23 in place of the foregoing side branch 51.

This embodiment basically provides the same effects as those of theother embodiments shown above. Presence of the foaming body 52 providedin the middle of the communicating path 23 communicating between the VSV31 and the equilibrium chamber 19 slows down the increasing anddecreasing rates of pressure in the equilibrium chamber 19. Fluctuationsof pressure in the equilibrium chamber 19 exhibits a smoother behaviorlike a sine wave, thus permitting control of pressure fluctuations ofthe liquid in the main liquid chamber 15 in response to the engine 1vibration, thus ensuring the same effects as those of the precedingembodiments.

As further another embodiment of the present invention, a variationshown in FIG. 10 is conceivable in addition to the above. In thisembodiment, a second diaphragm 18 has stopper-like projections 114 and114′ on the upper and lower sides near the center of the seconddiaphragm 18 with a view to improving the deformation rigidity (springconstant) of the second diaphragm 18. The tip end of the upper one (114)from among the upper and lower projection 114 and 114′ comes intocontact with a partition plate 124 separating the main chamber 15 fromthe third liquid chamber 123. The tip end of the lower one (114′) comesinto contact with a partition plate 39 forming the lower surface of theequilibrium chamber 19 as communicates with a pressure control portionas shown with a dush line.

As a result, upon introduction of a negative pressure or the atmosphericpressure into the equilibrium chamber 19 through the communication path23 provide with the side branch to cope with idling vibration, thesecond diaphragm 18 deforms, i.e., vibrates by deformation of theprojections 114 and 114′, or by deformation (displacement) of the flatportion 112 not having the projections 114 and 114′. To cope with engineshake, on the other hand, the stopper-like projections 114 and 114′prevent deformation (displacement) of the entire diaphragm 18, andconsequently, the spring constant (deformation rigidity) of the seconddiaphragm shows a higher value than that of a first diaphragm 20provided on the auxiliary chamber 17 side. That is, the liquid in themain chamber 15 flows through the first orifice 16 toward the auxiliarychamber 17. As means to improve the deformation rigidity (springconstant) of the second diaphragm 18, there is conceivable a variationof configuration having a spring 115 having a prescribed springconstant, provided below the second diaphragm 18, i.e., on theequilibrium chamber 19 side, and always operating so as to push back thesecond diaphragm 18 toward the third liquid chamber 123 (see FIG. 11).

In the case of engine shake which is vibration of a frequency lower thanthat of the above-mentioned idling vibration, the liquid is caused toflow through the first orifice 16 connecting the main chamber 15 and theauxiliary chamber 17, thereby absorbing and isolating engine shake. Inthis embodiment, more particularly, as shown in FIG. 10, the switchingmeans 25 is first operated to bring the equilibrium chamber 19 into thestate open to the open air, thus permitting free vibration of the seconddiaphragm 18 provided at the equilibrium chamber 19. When engine shakeis entered into the main chamber in this state, fluctuations of pressureof the liquid in the main chamber 15 propagate through the secondorifice 125 and the third liquid chamber 123 to the second diaphragm 18.However, because the second diaphragm 18 has the stopper-likeprojections 114 and 114′ near the center as shown in FIG. 10, and theupper and lower tip ends of these projections 114 and 114′ are always incontact with the partition plate 124 between the main chamber 15 and thethird liquid chamber 123 and with the partition plate 39 forming thelower surface of the equilibrium chamber 19, it is difficult for thesecond diaphragm 18 itself to deform (displace) in the verticaldirection. As a result, the liquid in the main chamber 15 flows throughthe first orifice 16 having a large diameter toward the auxiliarychamber 17 having a wall thereof formed by the easily deformable firstdiaphragm 20. A high damping property (a high damping force) of thisvibration isolating apparatus is available from the flow of the liquidto the first orifice 16, and this high damping force inhibits (damps)the foregoing engine shake. And, the constitution of this embodiment canprevent the generation of such wrong conditions that the vibrationabsorbing characteristic changes due to fatigue of the diaphragm, andthe equilibrium chamber is lost due to adhesion phenomenon of thediaphragm to the wall thereof. While, in this embodiment, the diameterof the second orifice 125 has been set at a value smaller than thediameter of the first orifice 16, the orifice may have a largerdiameter, depending upon the degree of rigidity of the second diaphragm18 forming the equilibrium chamber 19. In other words, it suffices thatthese diameters take values such that, in the state open to the open airof the equilibrium chamber 19, the liquid flows preferentially towardthe first orifice 16.

In this embodiment, the communication path 23 in the pressure controlportion as encircled with dush line may provide with a resistanceportion, and the atmospheric pressure duct line may provide with anexpansion chamber. Then, the expansion chamber may be used with the sidebranch.

Now, another embodiment of the present invention will be described withreference to FIG. 11. This embodiment has the same basic constitution asthe embodiment shown in FIG. 10. It is characterized in that there isprovided a spring 115 serving to push back the second diaphragm 18toward the main chamber 15 on the back of the second diaphragm 18. Morespecifically, as shown in FIG. 11, the vibration isolating mechanism 14basically comprises a main chamber 15, provided below the insulator 13,sealing a liquid which is an incompressible fluid, an auxiliary chamber17 connected to the first chamber 15 via a first orifice 16 having alarge diameter, and partitioned by a soft first diaphragm 20, an airchamber 21, provided below the auxiliary chamber 17 via the firstdiaphragm 20, always receiving air, a third liquid chamber 123 providedbelow the first chamber 15 and partitioned by a plate 124, a secondorifice 125, provided at the plate partitioning the third liquid chamber123 and the main chamber 15, and comprising a plurality of openings, asecond diaphragm 18, provided below the third liquid chamber 123, andpartitioning from the third liquid chamber 123, and an equilibriumchamber 19 partitioned via the second diaphragm from the third liquidchamber 123.

In this basic constitution, the second diaphragm 18 partitioning theequilibrium chamber 19 and the third liquid chamber 123 is basicallymade of a rubber-film-like member, and has a disk-shaped reinforcingplate 118 for protecting this rubber film, provided on the back (lowerside). The reinforcing plate 118 is formed by a rigid body such as ametallic plate. A spring 115 operating to push back (push up) the seconddiaphragm 18 always toward the third liquid chamber 123 is provided viathe reinforcing plate 118, as shown in FIG. 11, at the reinforcing plate118 of the second diaphragm 18 having the configuration described above.This spring 115 comprises a coil spring in most cases. The coil spring115 is set so as to always push up the second diaphragm and eventuallyensure the volume of the equilibrium chamber 19.

A plate 124 provided above the equilibrium chamber 19 and the seconddiaphragm 18 partitioning and forming a part of the equilibrium chamber19 and between the main chamber 15 and the third liquid chamber 123forms a rigid protector. This plate 124 serving also as a protectorprevents the lower end 166 of the upper coupling member 11 from hitting(coming into contact with) the second diaphragm 18 partitioning andforming the third liquid chamber 123 and the equilibrium chamber 19 whenlarge-amplitude vibration is entered into the upper coupling member 11connected to the vibrating body and the insulator 13. That is, the plate124 serves as a down stopper of this vibration isolating apparatus andalso serves to protect the second diaphragm 18. A plurality of openingsare provided at positions off this plate 124 having the aforesaidconstitution, and forms the second orifice for causing the liquid in themain chamber 15 to flow into the third liquid chamber 123 with theseplurality of openings.

Switching means 25 operating to introduce a negative pressure or theatmospheric pressure in an appropriately switched state into theequilibrium chamber 19 having the constitution as described abovecomprises a switching valve 31 comprising a three-way valve or the likeand a solenoid 32 driving the switching valve 31, as in the pressurecontrol portion of the embodiment as encircled with a dashed line inFIG. 11. Control means 41 for controlling a switching operation of thisswitching means comprises a microcomputer (CPU) formed basically bycomputing means such as a microprocessor unit as in the firstembodiment, and detects vibration from a vibrating body such as anengine to control a switching operation of the switching means inresponse to the vibration.

Now, operations of the apparatus of the embodiment having theconstitution as described above will be described below. Theconstitution is basically the same as that shown in FIG. 10. Thisembodiment is characterized in that, regarding the second diaphragm 18partitioning the third liquid chamber 123 and the equilibrium chamber19, the constitution around the same comprises the rubber-film-likesecond diaphragm 18, and the spring 115 operating so as to push back thesecond diaphragm 18 always toward the third liquid diaphragm 123. Morespecifically, to cope with idling vibration, the switching means 25 isoperated to alternately introduce an engine negative pressure and theatmospheric pressure into the equilibrium chamber 19, thereby causingthe second diaphragm 18 to deform to resist to spring reaction of thespring 115 and vibrating the liquid in the third liquid chamber 123 toeventually cause an increase in the liquid pressure in the main chamber15. As a result, the dynamic spring constant for the entire vibrationisolating apparatus is reduced against idling vibration, thus permittingisolation of the idling vibration.

To cope with engine shake, fluctuations of liquid pressure in the mainchamber 15 is transmitted to the third liquid chamber 123 via the secondorifice containing the plurality of openings by bringing the equilibriumchamber 19 into the state open to the open air. However, because thesecond diaphragm 18 provided below the third liquid chamber 123 isalways pushed up by the spring 115, the second diaphragm 18 does notdisplace (deform) under the effect of this spring reaction (resistancedrag) of the spring 115. As a result, the liquid in the main chamber 15flows through the first orifice 16 toward the auxiliary chamber 17having a portion of wall thereof formed by the easily deformable firstdiaphragm 20. A high damping property is available from this flow of theliquid in the main chamber 15 into the first orifice 16, thus permittingeventual damping (inhibition) of engine shake.

Further, in the pressure control portion the atmospheric pressure ductline may provide with an expansion chamber, and the communication pathmay provide with a side branch or a resistance portion. Then, theexpansion chamber may be used together with the side branch.

What is claimed is:
 1. A liquid-sealing type vibration isolatingapparatus comprising: a coupler configured to be attached to a vibratingbody; a holder configured to be attached to a vehicle body side; aninsulator provided between said coupler and said holder that absorbs andisolates vibration from said vibrating body; and a vibration isolatingmechanism which directly follows said insulator and which is formed witha liquid chamber containing a liquid in the form of an incompressiblefluid, wherein said vibration isolating mechanism includes a mainchamber having a wall that is formed by a part of the insulator and thatseals the liquid, an auxiliary chamber connected to said main chambervia a first orifice, wherein said liquid flows through said firstorifice and said auxiliary chamber is formed by a first diaphragm, anequilibrium chamber divided from said main chamber via a seconddiaphragm which allows the volume in the equilibrium chamber to change,a partition plate located in the main chamber and dividing the mainchamber into a main portion and a sub-portion with the sub-portion beinglocated between the main portion and the second diaphragm, the partitionplate having a second orifice formed therein which allows fluid to flowbetween the main portion of the main chamber and the sub-portion of themain chamber, a switching mechanism which switches a pressure in saidequilibrium chamber alternatively to a negative pressure or atmosphericpressure in synchronization with engine vibration, wherein the switchingof the pressure in said equilibrium chamber causes said second diaphragmto vibrate in synchronization with engine vibration, and a controlmechanism which controls the switching operation of said switchingmechanism.
 2. The liquid-sealing type vibration isolating apparatusaccording to claim 1, wherein said coupler is an inner cylinder; saidholder is an outer cylinder; said insulator is provided around saidinner cylinder between said inner cylinder and said outer cylinder; saidvibration isolating mechanism is provided around said insulator; and thefirst diaphragm separates an air chamber from said auxiliary chamber. 3.A liquid-sealing type vibration isolating apparatus according to claim1, further comprising an elastic stopper member located in the mainchamber, the elastic stopper member and the partition plate beingconfigured and disposed so as to protect the second diaphragm from largeamplitude vibrations when large amplitude vibrations enter the mainchamber from the vibrating body.
 4. A liquid-sealing type vibrationisolating apparatus according to claim 1, wherein the second diaphragmhas a higher deformation rigidity than the first diaphragm.